Computer is an electronic machine that is used to solve different kinds of problems according to a set of instructions given to it. Computer consists of different units that perform various functions. All the operations of the computer are controlled by the program instructions. These program instructions are known as software. A system is a group of related components that make up a body to perform a specific function. Therefore computer system is defined as:

The computer along with various units and software that performs different activities in data processing are collectively known a computer system. A computer system is divided into two sub-systems:

1. Computer Software
2. Computer Hardware

Computer Software

A set of instructions given to the computer in machine code that tells the computer what to do and how to perform the given task of the user is known as computer software.

 OR

A set of instructions given to the computer in machine code to solve problems or to control different operations of the computer is known as computer software.

the sofware is developed in computer programming languages. You can not feel, touch or see software inside the computer memory.

Computer Hardware

The physical parts of a computer are known as computer hardware. You can touch, see and feel the hardware. The hardware consists of electronic circuits and mechanical equipment etc. used to perform various functions in the computer. The hardware components are:

1. Input devices
2. Output devices
3. Central Processing Unit (CPU)
4. Memory unit
5. Storage devices

Components of Computer

The internal architechtural design of computers differs from one system model to anohter. However the basic components and their functions are same for all computer systems. The construction of a typical comupter (PC) is very simple. It contains different components. Each components performs a specific function in the computer.

Input Devices

The devices that are used to enter data and instructions into the computer are called input devices or units. In old computers the punched card readers, paper tape readers were used as input devices. Now-a-days the most commonly used input devices are Keyboard and Mouse.

Output Devices

The computer processes the given input data and gives the output. The devices that are used to get output from a computer in readable from are called output devices. A number of output devices are available. Some commonly used output devices are video display units (VDU) and printers.

Central Processing Unit

Central Processing Unit is simply called as CPU. It is the main components of the computer and it is also called the Processor. The processor used in microcomputer is referred to as Microprocessor. CPU is considered the brain of the computer. It performs all operations of data according to program’s instructions. It executes the program instructions and tells other parts of the computer what to do. The CPU fetches instructions of program from main memory and executes them one by one. The CPU also has the ability to decide which instruction will be executed next. The speed of the CPU is measured in Mega Hertz (MHz) or Giga (or more).

The CPU is divided into two main prart of sub-units. These are:

1. Control Unit (CU)
2. Arithmetic Logic Unit (ALU)

1. Control Unit (CU)

The control unit is the most important component of the CPU. It controls and coordinates the activities of all the other units of the computer. The control unit is considered as the logical hub of the computer. It acts as a central nervous system for the other components of the computer.

For example the control unit receives the data and instructions from the input device and stores them in the main memory. It performs all these functions by issuing commands to the relevant unit of the computer.

The control unit also controls the execution of instructions given to the computer. It fetches the instructions and data from the memory unit. It decodes and executes the instructions one by one.

2. Arithmetic Logic Unit (ALU)

Arithmetic Logic Unit or simply ALU is another important component of CPU. It performs the arithmetic and logical operations on the data. When the control unit encounters and instruction related to perform arithmetic or logical operation on data, it passes that instruction to ALU.

• In arithmetic operations ALU performs the addition, subtraction, multiplication and division.
• In logical operations ALU compare the numerical data as well as alphabetic data. For example, it checks whether first number is greater than second, less than second or equal to second etc. It must be noted that some of the logical operations can be done on test data. For example when you want to search a word in a document., the CPU matches each word of the docum ent with the given word. Actually the ALU compares each word of document with the given word through relational equal operator (=).

The ALU consists of a number of registers and adder circuits. A register is a temporary storage device which holds data and instruction as long as it is being interpreted (decoded) and executed. When the data and instructions are fetched from main memory for processing, these have to be stored in one of the registers of the CPU.

The keyboard is the most commonly used input device. It is used to feed data and instructions into a computer. It is similar to an electric typewriter. A keyboard contains keys for each alphabetic characters, digits and special characters. The data and instructions are feed into the computer by pressing the related keys on the keyboard. The keyboard having some additional keys for specific functions. Keyboard used with personal computer typically have from 101 to 105 keys.

On laptop and many other handheld computers, the keyboard is built into the top of the system unit. Usually, these keyboards are smaller in size and have fewer keys such as 85 keys.

Some old type computers have built-in keyboards. Now-a-days, the computer has a separate keyboard. It is easily plugged in computer. A keyboard is connected to the serial or USB port on the system unit. A standard computer keyboard is also referred to as QWERTY keyboard. This name represents the first left most letters on the top alphabetic line of the keyboard spell. Some advanced keyboards do not require the cable to connect with the cable. They enter data into the computer through wireless technologies such as radio waves or infrared light waves. These type of keyboards are known as cordless or wireless keyboards.

Division of Keyboard

A keyboard may be divided into four area. There are:

1. Alphanumeric keypad or typewriter area.
2. Numeric keypad.
3. Screen Navigation keys.
4. Editing keys.
5. Function keypad.

1. Alphanumeric Keypad

This area is like a typewrite, it is because this area of keyboard is referred to as Typewriter Area. The user uses this area to enter general information into the computer. Typists usually use this area of keyboard. This area consists of:

• Alphabetic character keys “A” to “Z” and lower case letters “a” to “z”.
• Numeric keys “0″ to “9″.
• Many other special keys like Spacebar, Enter key, Ctrl key etc.

2. Numeric Keypad

A set of numeric keys and arithmetic operator keys on the right of keyboard that are similar to calculator keys is referred to as Numeric Keypad. It also has an extra Enter key and Num Lock key. The Num Lock key is used to activate or deactivate the numeric keypad. The numeric keypad is mostly used for numeric data entry.

3. Screen Navigation Keys

The keys that are normally used in word processor or other application programs to move cursor into the document on the screen are referred to as navigation keys. The most important navigation keys are:

4. Editing Keys

The keys that are normally used in word processor or other application programs for editing (modifying) the document are referred to as editing keys. The most important editing keys are:

5. Function Keys

There are 10 or 12 function keys on the top of keyboard that are labeled as F1, F2,…….. F12. These keys are referred to as Function Keys. These are used to perform special functions. The function of each key depends upon the software being used on the computer. The designer of the software assigns these keys in his software as shortcut commands or keys to perform specific task. For example, in most software the function key F1 is used to get online help about the software running on the computer.

Many keyboards also have a Windows Key. When Windows key is presses, Start Menu of Windows is displayed.

The advanced keyboards also include buttons that allow the user to access the computer’s CD or DVD drive. Adjust speaker volume, open an e-mail program, start a web browser and search the Internet. Some keyboards also provide the USB ports used to plug the USB device directly to the keyboard instead of system unit.